1. Field of the Invention
The present invention relates to a method of and a apparatus for recording and reading a radiation image, and more particularly to a method of and an apparatus for recording the image of a relatively long subject such as the spine, or vertebral column, of a human body on an elongate stimulable phosphor sheet, and reading the recorded image information.
2. Prior Art
There have recently been developed radiation image information recording and reproducing systems for recording the radiation image of a subject, such as a human body, on a stimulable phosphor sheet, then scanning the stimulable phosphor sheet with stimulating light to cause it to emit light, photoelectrically reading the emitted light to produce an image signal, and processing the image signal to obtain a radiation image of the object which may be used for medical diagnosis (see, for example, Japanese Laid-Open Patent Publications Nos. 55-12429, 56-11395, 55-163472, 56-104645, 55-116340, etc).
In the radiation image information recording and reproducing systems, the final radiation image may be reproduced as either a hard copy image or a visible image on a CRT. Since the stimulable phosphor sheet employed in those systems is not a final image carrier for recording image information, but a temporary image carrier from which image information will eventually be transferred to a suitable recording medium. Therefore, the stimulable phosphor sheet may be repeatedly used, and such repeated use of the stimulable phosphor sheet is highly economical.
In order to use a stimulable phosphor sheet again, any residual radiation energy that may remain on the stimulable phosphor sheet from which the emitted light has been read is discharged according to the process disclosed in Japanese Laid-Open Patent Publications Nos. 56-11392 and 56-12599, for example. After the residual radiation image has been erased, the stimulable phosphor sheet is put to use for recording radiation image again.
There has been proposed a built-in type radiation image information recording and reading apparatus in which a stimulable phosphor sheet is circulated for repetitive use, as disclosed in Japanese Laid-Open Patent Publication No. 59-192240. More specifically, the proposed apparatus comprises a circulatory feed means for feeding, along a circulatory path, a stimulable phosphor sheet which can record a radiation image, an image recording unit disposed in the circulatory path for applying a radiation bearing radiation image information of an object to the stimulable phosphor sheet to record the radiation image information on the stimulable phosphor sheet, an image reading unit disposed in the circulatory path and including a stimulating light source for emitting stimulating light to scan the stimulable phosphor sheet on which the radiation image information has been recorded by the image recording unit and a photoelectric reading means for reading light emitted from the stimulable phosphor sheet scanned by the stimulating light to produce an image signal indicative of the recorded radiation image information, and an erasing unit disposed in the circulatory path for discharging any residual radiation energy from the stimulable phosphor sheet before new radiation image information is recorded on the stimulable phosphor sheet after the previous radiation image information has been read by the photoelectric reading means. The stimulable phosphor sheet is circulated along the circulatory path through the image recording unit, the image reading unit, and the erasing unit for repetitive use.
The proposed radiation image information recording and reading apparatus allows successive items of radiation image information to be recorded and read efficiently.
The built-in type radiation image information recording and reading apparatus is designed to record radiation image information with respect to various body parts of patients, including the chest, abdomen, limbs, etc. Stimulable phosphor sheets used to record such radiation image information are selected in sizes (e.g., a half size) depending on the body parts to be recorded.
There is a recent demand for the diagnosis of entire vertebral columns using the built-in type radiation image information recording and reading apparatus. To diagnose an entire vertebral column using the built-in type radiation image information recording and reading apparatus, the image of the vertebral column may be divided into two portions, which are recorded respectively on two stimulable phosphor sheets. However, the recording process is complex and inefficient since two different parts of the vertebral column must be recorded independently. If the patient moved while the image recording unit is moving after one image has been recorded, then no accurate subsequent image would be recorded, and hence no correct diagnosis could be carried out.
One solution would be to use an elongate stimulable phosphor sheet long enough to cover the image of a relatively long subject such as a human spine, or vertebral column, in a built-in type radiation image recording and reading apparatus. However, it would be time-consuming to read the recorded image and erase residual image information from the elongate stimulable phosphor sheet in a small-size built-in type radiation image recording and reading apparatus, making it virtually difficult to shorten the cycle time required to process the stimulable phosphor sheet.
According to one application, a plurality of elongate stimulable phosphor sheets would be successively employed in a small-size built-in type radiation image recording and reading apparatus. Usually, different periods of time are required to record a radiation image on a stimulable phosphor sheet, read a recorded radiation image from a stimulable phosphor sheet, and erase residual image information from a stimulable phosphor sheet. To cope with such different periods of time, it is necessary to provide a standby zone between the image recording unit, the image reading unit, and the erasing unit for holding stimulable phosphor sheets in readiness for next processing operation.
The standby zone in the small-size built-in type radiation image recording and reading apparatus has a bent configuration with a sharply curved path. When an elongate stimulable phosphor sheet is held in the sharply curved path in the standby zone, the stimulable phosphor sheet tends to be largely curved and sometimes damaged. It is desirable to hold a stimulable phosphor sheet in a straight path so that the stimulable phosphor sheet will not have a curling tendency.